Process for producing α,β-unsaturated carboxylic acid polymer

Abstract

A less colored α, β-unsaturated carboxylic acid polymer having a relatively small molecular weigth and a sharp molecular weight distribution is produced by supplying an α,β-unsaturated carboxylic acid monomer and a hydrogensulfite from one side of a reaction column and simultaneously supplying an oxygen-containing gas concurrently with the monomer to the reaction column. The polymer obtained is preferably used as a dispersant and an antiscaling agent.

What is claimed is: 
     
       1. A process for producing a polymer of at least one α,β-unsaturated carboxylic acid or salt thereof wherein (a) at least one monomer comprising one or more α,β-unsaturated carboxylic acids or salts thereof as essential components are polymerized or copolymerized with (b) at least one other hydrophilic monomer copolymerizable with (a), by supplying (a), (b) and a hydrogensulfite from one side of a reaction column and   simultaneously supplying an oxygen-containing gas concurrently with (a) and (b) to said reaction column to form a film stream of (a) and (b) on the inner wall of said reaction column by means of the gas stream of said oxygen-containing gas to effect polymerization.   
     
     
       2. The process as set forth in claim 1, wherein a rising film stream is made of (a) and (b) by holding said reaction column upright and supplying (a) and (b) and said gas from the bottom of said reaction column. 
     
     
       3. The process as set forth in claim 1, wherein a descending film stream is made of said film stream of (a) and (b) by holding said reaction column upright and supplying (a) and (b) and said gas from the top thereof. 
     
     
       4. The process as set forth in claim 1, wherein said polymer of at least one α,β-unsaturated carboxylic acid or salt thereof is selected from the group consisting of acrylic acid, methacrylic acid, α-halogen-substituted acrylic acid, itaconic acid, fumaric acid and maleic acid. 
     
     
       5. The process as set forth in claim 1, wherein (b) is selected from the group consisting of, acrylamide, methacrylamide, acrylonitrile, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, vinyl sulfonic acid, and sodium styrene sulfonate. 
     
     
       6. The process as set forth in claim 1, wherein the hydrogensulfite is selected from the group consisting of alkali metal salts, ammonium salt and triethanolamine salt. 
     
     
       7. The process as set forth in claim 1, which comprises supplying acrylate monomer(s) (I) containing (i) 20 to 100% by mole of an alkali metal acrylate; (ii) at most 80% by mole of one or more monomers selected from the group consisting of acrylamide, 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate; and (iii) at most 30% by mole of a hydrophilic monomer capable of copolymerizing with the above components (i) and (ii), the total of the components (i), (ii) and (iii) being 100% by mole, and a hydrogensulfite (II) in an amount within the range of 0.008 to 0.4 mole per mole of said acrylate monomer(s) (I) each in the form of an aqueous solution to a reaction column separately or in the form of a combined mixture, wherein the concentrations of the aqueous solutions of the acrylate monomer(s) (I) and the hydrogensulfite (II) are 10 to 60% by weight and 1 to 40% by weight, respectively. 
     
     
       8. The process as set forth in claim 1, wherein the thickness of the film stream on the inner wall of the reaction columns is 0.2 to 5 mm. 
     
     
       9. The process as set forth in claim 1, wherein (a) and (b) are supplied at a rate of 0.001 to 2 m 3  /hr, the gas stream is supplied at a rate of 0.01 to 30 m 3  /min and the gas and the thin film stream in the reaction column are transported at rates of 2 to 100 m/sec and 0.2 to 20 m/min, respectively. 
     
     
       10. The process as set forth in claim 1, wherein the inside of the reaction column is maintained at a temperature of 5° to 80° C.